"We don't have victory. We're dropping things all over the place. Who knows what they are hitting? Who knows how many people are being killed? Who knows if they're the right people?" Trump told a veterans group, the Retired American Warriors PAC, in Herndon, Virginia.

The US-led counter-ISIS coalition has conducted over 15,000 airstrikes in Iraq and Syria.

Trump's comments stand in stark contrast to how the US military has described the air campaign. Lt. Gen. Jeffrey Harrigan, the commander of US air forces in the Middle East, said last month it is "the most precise air campaign in history."

"We have been able to deliver weapons with precision since the beginning of this war," Harrigian added.

Read More

Harrigian went on to stress that the US was getting an accurate picture of the situation on the ground, saying the US and its allies were "taking great lengths to understand that we know what the target is," highlighting the deployment of intelligence, surveillance, and reconnaissance assets that allow US forces to observe a target for days.

Trump's suggestion that the US military might not be striking its intended targets comes as US defense officials have drawn distinctions between US targeting efforts and the efforts of the Russian and Syrian regime air forces. Officials have said the Russian and Syrian attacks have been indiscriminate and killed civilians.

US officials point to the fact that over 90% of weapons dropped by the US and its allies are "smart bombs" that are either laser or GPS guided munitions. The Russians on the other hand use less sophisticated gravity bombs that are considered much less precise. The US and non-government organizations have also accused the Syrian regime of using "barrel bombs," an even cruder weapon.

President Barack Obama has described the Russian and Syrian air campaign as "'barbarous" and the Chairman of the Joint Chiefs, Gen. Joseph Dunford, told Congress that the Russians were responsible for an airstrike against a UN humanitarian aid convoy.